j9fd3s

iTrader: (3)

1. the Japanese tuners do things slightly differently, in that they are usually running a PFC, or other ecu tuning, and colder spark plugs before they run a mid-pipe. so yes, you can certainly solve the problem.
2. there are two turbo designs, the 255/265ps turbos, which are 1992-2003, and then the 99+ 280ps turbos.

mikejokich

iTrader: (1)

I would add, there are now three designs. Hitachi put out the KAI SP version of these turbos several years ago, which I now use. These are factory turbos directly from Hitachi. They move 12% more air, have a larger shaft, better seals, and lastly have a larger internal wastegate directly from the factory, I have no boost creep since I installed these with a very free flowing 3.5-3.0" exhaust with a large bellowed downpipe, ported exhaust manifold, and racing Vibrant metal cat. IMO, I would never choose any other version for a stock Hitachi twin replacement. Why would you for approx. $300 more.
Mike

DaleClark

iTrader: (55)

If you really want to get down to it, there are 3 turbos that were on the cars stock -

N3A1 - on 93-95 cars, prone to bad cracking on the turbine housings.
N3C1 - on 96-2002 255hp/265hp cars. Some 95's may have them too. Much less prone to cracking due to a higher nickel content in the cast iron. Wastegate actuators are gold colored instead of green (cosmetic) and pills for the turbo lines are built into the nipple at the compressor housing.
N3G1 - the "99 Twins", updated with the abradable seal on the compressor housing, different sized turbine wheels, etc. These were on the 99+ 280hp cars. Same upgrades as the N3C1 turbos (better turbine housings, gold actuators, built-in pills).

A lot of the boost creep is the stock ECU's boost control solenoids. They have a fixed map - at x rpm, do y duty cycle. There's no feedback (or at least no obvious feedback) with actual boost pressure. When you open up the exhaust the ECU has no idea and still runs the boost control like the restrictive stock system is in place. This easily leads to spiking at the transition and boost can creep at higher RPM's. Many times changing the pill sizes or going with an aftermarket boost controller can solve this issue.

Porting the waste gates is necessary with boost creep with proper boost control. There's no hard and fast point saying do x, you have to port the wastegate. A mid pipe does open up things a HUGE amount and will lead to creep more often than not, but some cars do fine, some creep like crazy. Lot of it is the health of the turbos, health of the engine, quality of the ECU's tune, etc. The N3A1 turbos with all the cracking can crack around the wastegate which lets exhaust gasses bypass the wastegate, somewhat acting like a port but also resulting in lazy spool.

Regardless, putting on a mid pipe is definitely a "you need to be this tall to ride this ride" mod. TONS of people in the 90's blew engines left and right with mid pipes, especially before the PowerFC and good ECU's were out.

Before going with a mid pipe, you need to have at least a PowerFC in place to be able to tune for it. An aftermarket boost controller or using the factory solenoids or MAC solenoids with the PowerFC and a Datalogit is also required.

Dale

j9fd3s

iTrader: (3)

the N3A1 was 1993 only, 1994+ has N3C1's, look it up in the parts catalog.

DaleClark

iTrader: (55)

One would think . My car came with N3A1's on it. I think I'm later in the production for 94, VIN ending in the 2000's I believe. Those are long gone now of course .

BTW the rear/secondary compressor housing has the model number stamped onto it.

I haven't found a good solid line for when Mazda started putting the N3C1's on the cars. At this point it's hard to tell since so many cars had turbos swapped out in the 90's.

Dale

adey

SO MUCH WIN in this thread... Thank you guys so much!

Before we go too far off topic, I'll assume that a parallel twin 80mm cat setup (FEED) will flow "too much" for the stock tune, thus requiring me to buy and install some kind of additional engine management...? Would it be safe to run on the OEM ecu and tune if I keep off the floorpan?

(What do people here use bedsides PFCs or other stand alone ECUs? Is there a middle way, or have I opened Pandora's box? Almost all the modified FDs sold here have PFCs in them!)

DaleClark

iTrader: (55)

As stated, every car is a little different. What works for one person won't work for another.

Good rule of thumb with the stock ECU is if your boost stays at 10psi MAX you are OK. In theory it can support more, but I wouldn't trust it.

You can run a full 4" exhaust on a stock ECU if you keep your foot out of it and drive like grandma. It's only when you go full throttle and are building up boost that you will get in trouble.

The PowerFC is popular for a reason - it's reasonably priced, super easy to install, is very flexible, and is very reliable. In Japan chip tuning is super popular where they put a new ROM chip in an ECU to support whatever mods you have on the car. You have some downsides, like you pretty much have to run an air pump or you will have a crappy idle, etc.

You can also go with a Haltech which are fantastic ECU's with a lot of power and much more modern design than the PowerFC. They do cost more and at this point in time there's not as much support for it in the RX-7 world, but it's growing more and more popular on the RX-7.

Dale

silverTRD

iTrader: (36)

Do cats do anything to reduce noise?

I have the rx7store mp and while it sounds nice, I’m wanting to put a hfc back in. The one I’m looking at is the Fabspeed 121mm x 112mm long so it will support my power level. Ideally I would use both the cat and keep the center muffler but once I add in the length of the reducers needed the cat is pretty long. I suppose I can add the cat into my racing beat exhaust, there should be room there.

Thoughts?

j9fd3s

iTrader: (3)

cat needs a heat shield, trust me, i've melted a couple carpets...

DaveW

Anything that has some inner texture/compartments will reduce noise. However, a small cat will have only a very small effect - think small straight-through glass-pack for reference.

silverTRD

iTrader: (36)

https://www.fabspeed.com/hjs-tuning-...l-directional/

this is is the one being recommended to me. The easiest place to put it would be in the racing beat exhaust.

Im glad I asked about the noise because now I know I don’t want to lose my large magnaflo muffler in the mp.

Topolino

iTrader: (2)

^Have you considered the GESi versions offered by Vibrant? P/n 7840 would seem to be a good fit for you. Fully fabricated w 4" inlet/outlet already, and 7.5" total length....
https://vibrantperformance.com/catal...Path=1527_1326

silverTRD

iTrader: (36)

I’ve considered them. I was recommended a 200 cell unit cat by my tuner. I’m not sure how that really makes a difference to be honest. I know the lower the cell count the more the unit is supposed to flow, and the higher cell count is better for removing emissions. But if a 300 cell cat is rated for 500-850 hp, I’m not sure how that applies.

Topolino

iTrader: (2)

^There will be a noticeable difference in exhaust odors w either choice compared to your current setup of cat-less. So that's a win right there. However, any add'l discussion is likely splitting hairs regarding ultimate performance gains; I.e., less than 3-4% at best.

That said, HJS is very reputable in the German high performance/aftermarket auto arena. If you can squeeze out a tad better flow (200 cpsi vs 300), and presumably w less back pressure overall, then that's the direction I'd go wout much further hesitation.

So, other than the midpipe location, I've also considered similarly mounting at that first, relatively straight section just aft of the midpipe-to-catback connection. Getting any high flow cat as far down the exhaust process chain is apparently preferred re: long term reliability of the cat. Can always insulate in that area as recommended above, too. Alternately, there is that existing straight section of our downpipe where the stock pre-cat used to reside. Would the metal catalyst hold up there where a traditional ceramic aftermarket unit would most assuredly degrade in short order? Hmmm, likely/maybe??

silverTRD

iTrader: (36)

I do have room for the cat in the downpipe but I do not want to put it there for the reasons you state. I feel it will take too much abuse that close to the turbo.
I'll take your advice and fab up some sort of heatshield j9fd3s.